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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Principle Of Snow Formation Large snowflakes can be formed by the collision of ice crystals within clouds (aggregation process) Smaller snowflakes are formed by the Bergeron-Findeisen process For snow to reach the ground the air temperature must be no more than 35.6 o F (2°C) Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Principle Of Snow Formation Contd One would expect the falling snow to melt as soon as the temperature rises above freezing, but this is not so. As the melting process begins, the air around the snowflake is cooled. The heaviest falls of snow tend to occur when the air temperature is between 32 and 35.6 o F (2°C) Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Features Of The TB323 LP More effective method of measuring snowfall Increase accuracy of measuring snowfall ± 2% based on the principle of the tipping bucket raingauge. Avoid freezing of gauge in cold climates. Hence, eliminates subsequent loss of precipitation records Gauge can be used for rainfall and snowfall (2 in 1) Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Features Of The TB323 LP Contd Snow sensor which activates the heating elements inside the raingauge only when snow events occur. Duty cycle heating to reduce power after initial warm up. Total power consumption is generally reduced by the combination of the above two features Copyright Snow Sensor

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Principle Of Operation Initial State Rainfall Only The Hydrological Services Tipping Bucket Raingauge (TB3) is recognised as the standard for measuring rainfall and precipitation in remote and unattended locations. The TB3 raingauge operates on the tipping bucket principle. A receiver of 200mm diameter collects the rainfall, which is strained by a metal gauze before being passed through the syphon to the tipping bucket measuring system. Tips of the plastic bucket occur with each 0.2mm, 0.5mm or 0.01 inch of precipitation collected. A reed switch detects these events and produces a momentary contact closure signal for: -logging in our Rainfall Data Logger -transmission by our Radio Reporting Raingauge, or -display on our Rainfall Counter Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Principle Of Operation Contd Snowfall State: The TB323LP kit is designed for use with the TB3 raingauge to accurately measure snowfall by converting snow into liquid. The device is basically a thermostatically controlled heating element, that raises the temperature of the interior of the raingauge, funnel and catch to avoid the freezing of the gauge in cold climates with subsequent loss of precipitation records. When the ambient temperature drops below a preset value (+ 4 o C), the snow sensor mode is activated. The heater elements remains off until snow is present in the catch area triggering the initial heating period (100% power) followed by 40% duty cycle until there is no snow remaining in the catch. At the completion of the heating cycle the unit will return to wait mode until triggered by a snow event. The system will be de- activated when temperature drops below (-10 o C) or above (+4.5 o C) nominal. This combination of duty cycle and snow sensor is designed to reduce power consumption. Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Test Data Experiment: The testing of the TB323LP was done in Hydrological Services environmental chamber. The environmental chamber was set at a steady temperature of –10 o C. Three heating elements were used. Two elements were placed below the funnel and the third element was placed at the base of the gauge beneath the bucket. To be more conservative in testing, Hydrological Services used shaved ice which is 3 times less dense than the water where snow is 10 times less dense than water. The raingauge funnel was loaded with shaved ice. Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Test Data Contd Two insulating sleeves were used one inside the enclosure and another outside the enclosure to reduce heat loss. The tests were repeated for 2 weeks to ensure repeatability and calibration of the raingauge was maintained. The bucket tips, funnel temperatures and ambient temperatures were recorded over the period to evaluate the effectiveness of the heating and melting processes. Copyright

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Issue1: 6/10/2004Hydrological Services Pty Ltd, Sydney, Australia Future Directions All operating parameters used by the Micro- processor controlled TB323LP are factory set. However, they may be adjusted by the customer using a RS232 to RS485 converter with appropriate procedure. SDI-12 comms will be shortly introduced to allow monitoring of the TB323LP heating unit as well as direct manual control or parameter modification in real-time. Copyright